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Biology - Unit 6 > Chapter 15 - Nervous Coordination + Muscles > Flashcards

Chapter 15 - Nervous Coordination + Muscles Flashcards

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1
Q

What is the nervous system?

A

System that uses nerve cells to pass electrical impulses. Target cells are stimulated by neurotransmitters

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2
Q

What is the hormonal system?

A

System that produces chemicals that are transported in the blood to target cells

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3
Q

Summarise the hormonal system

A

Communication by chemicals
Transmission by blood
Transmission slow
Hormones travel to all parts but only target cells respond
Response widespread, slow and long lasting
Effect may be permanent and irreversible

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4
Q

Summarise the nervous system

A 
Communication by nerve impulses
Transmission by neurones
Transmission rapid
Impulses travel to specific body parts
Response localised, rapid and short lived
Effect temporary and reversible
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5
Q

What are neurones?

A

Specialised nerve cells adapted to rapidly carry electrochemical changes called nerve impulses/action potentials

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6
Q

What is a mammalian motor neurone made up of?

A
  • Cell Body
  • Dendrons
  • Axon
  • Schwann Cells
  • Myelin sheath
  • Nodes of Ranvier
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7
Q

Describe the cell body of neurone

A

Contains all usual organelles with large amounts of RER for production of neurotransmitters

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8
Q

Describe dendrons of a neurone

A

Extensions of the cell body that divide into dendrites that carry nerve impulses towards the cell body

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9
Q

Describe the axon of a neurone

A

A single long fibre carrying a nerve impulse away from a cell body

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10
Q

Describe Schwann cells of a neurone

A

Cells that surround the axon, protecting, providing insulation and carrying out phagocytosis

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11
Q

Describe the myelin sheath of a neurone

A

Covers the axon and is made of Schwann cells with membranes rich with myelin

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12
Q

Describe the nodes of Ranvier of a neurone

A

Constrictions between adjacent Schwann cells where there is no myelin sheath

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13
Q

What are the three types of neruones

A

Sensory
Motor
Intermediate/Relay

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14
Q

What is a sensory neurone?

A

A neurone that transmits nerve impulses from a receptor to a motor neurone

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15
Q

What is a motor neurone?

A

A neurone that transmits nerve impulses from an intermediate/relay neurone to an effector

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16
Q

What is a intermediate/relay neurone?

A

A neurone that transmits nerve impulses between neurones

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17
Q

What is a nerve impulse?

A

A self-propagating wave of electrical activity that travels along an axon membrane

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18
Q

What are the two ions involved in nerve impulses?

A

Na+ and K+

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19
Q

How are Na+ and K+ ions moved across the cell membrane?

A
  • Phospholipid bilayer prevents simple diffusion
  • Channel proteins by facilitated diffusion
  • Sodium-potassium pump by active transport
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20
Q

What is the resting potential of a human neurone?

A
  • 65mV
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21
Q

How is resting potential established?

A
  • Sodium actively transported out and potassium actively transported in by sodium-potassium pump
  • Active transport of 3 sodium ions for every 2 potassium
  • More sodium outside creating electrochemical gradient
  • Diffusion still occurs, but sodium gates closed
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22
Q

Define action potential

A

A change that occurs in the electrical charge across the membrane of an axon when it is stimulated and a nerve impulse passes

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23
Q

Describe an action potential

A
  • Stimuli causes Na+ ions to enter the start of the neurone
  • Makes membrane potential less negative
  • If it reaches threshold (-50mV), Na+ channels open
  • Therefore more Na+ ions diffuse into the neurone, therefore membrane potential becomes positive (depolarised)
  • The membrane potential reaches +40mV
  • Then the Na+ channels close, the K+ channels open
  • Therefore K+ ions diffuse out, therefore membrane potential becomes negative (repolarised)
  • Too many K+ ions move out, so the membrane potential becomes more negative than normal (hyperpolarised)
  • Refractory period
  • One action potential = depolarisation, repolarisation, hyper-polarisation
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24
Q

Define depolarisation

A

Temporary reversal of charges on the cell surface membrane of a neurone that takes place when a nerve impulse is transmitted

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25
Q

Define repolarisation

A

Return to the resting potential in the axon of a neurone after an action potential

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26
Q

How is a myelinated axon different to an unmyelinated axon

A

Each axon has sheaths of myelin creating nodes of Ranvier where action potentials occur. This speeds up the action potential due to saltatory conduction

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27
Q

Define saltatory conduction

A

Propagation of a nerve impulse along a myelinated dendron or axon in which the action potential jumps from one node of Ranvier to another

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28
Q

What is a generator potential?

A

The first action potential

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29
Q

What are the three factors affecting the speed of an action potential?

A
  • Myelin sheath
  • Diameter of axon
  • Temperature
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30
Q

How does a myelin sheath affect the speed of an action potential?

A

Increases speed of action potential as action potential jumps from one node of ranvier to another

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31
Q

How does the diameter of an axon affect the speed of an action potential?

A

Greater diameter increases speed of the action potential due to less leakage of ions from diffusion

32
Q

How does temperature affect the speed of an action potential?

A
  • Higher temperature results in more diffusion due to more kinetic energy
  • Active transport energy comes from ATP produced from respiration. Enzymes act more rapidly at higher temperatures
  • Faster action potential unless temperature denatures enzymes
33
Q

What is the all or nothing principle of a action potential?

A

A threshold value exists where no action potential occurs below this. Anything above generates an action potential

34
Q

Why can we not perceive the size of a stimulus from a lone action potential?

A

They are all the same size and of the same strength

35
Q

How can an organisms perceive the size of a stimulus from an action potential?

A
  • Number of impulses (larger stimulus produces more impulses)
  • Different neurones with different thresholds and brain determines size
36
Q

Define voltage gated channel

A

Protein across a cell surface membrane that opens up and closes according to changes in the electrical potential across a membrane

37
Q

What are the three purposes of the refractory period?

A
  • Propagation in one direction
  • Produces discrete, separate action potentials
  • Limits the number of action potentials hence limiting strength of a stimulus
38
Q

Define effector

A

An organ that responds to stimulation by a nerve impulse resulting in a change or response

39
Q

Define synapse

A

A junction between neurones in which they do not touch but have a narrow gap called the synaptic cleft where a neurotransmitter passes

40
Q

Summarise the process of synaptic transmission (using acetylcholine as the neurotransmitter)

A
  • Action potential reaches presynaptic neurone
  • Ca2+ channels open and ions enter presynaptic neurone
  • Vesicles with acetylcholine move to presynaptic membrane
  • Bind with membrane and release acetylcholine into cleft
  • This diffuses across cleft and binds to complementary receptors on postsynaptic membrane
  • Na+ channels open, and ions enter
  • AP occurs if threshold reached
41
Q

How is the process of synaptic transmission returned to rest (using acetylcholine as the neurotransmitter)?

A
  • Enzyme breaks down neurotransmitter (acetycholinesterase breaks down acetylcholine into ethnic acid and choline)
  • Diffuses back into presynaptic neurone
  • ATP reforms acetylcholine and actively transport Ca2+ ions out
42
Q

Why does synapses ensure unidirectionality?

A

Only one end (presynaptic) releases neurotransmitters and one end (postsynaptic) has receptors

43
Q

State and describe the two types of summation in synaptic transmission?

A
  • Spatial summation where a number of presynaptic neurones release enough neurotransmitter to exceed threshold value of postsynaptic neurone
  • Temporal summation where single presynaptic neurone releases neurotransmitter repeatedly over time to exceed threshold value of postsynaptic neurone
44
Q

How do inhibitory synapses operate?

A
  • Neurotransmitter binds to chloride ions protein channels
  • Chloride ion channels open and Cl- moves in by facilitated diffusion
  • Also causes K+ protein channel to open and K+ ions move out into synapse
  • Negatively charged chloride ions moving in and positively charged potassium ions moving out cause hyper polarisation with membrane potential -80mv
  • Less likely new AP will form as more sodium ions needed
45
Q

How do synapses filter out low level stimuli?

A
  • Not enough neurotransmitter released so less Na+ ion channels open
  • Less Na+ ions enter postsynaptic neurone so threshold not reached
46
Q

What are excitatory synapses?

A

Synapses that produce new action potentials

47
Q

What are the two functions of synapses?

A
  • Single impulse on neurone initiate number of new impulses at different neurones to allow single stimulus to create a number of simultaneous responses
  • Number of impulses combined at synapse allowing nerve impulses from receptors reacting from different stimuli to contribute single response
48
Q

What is a cholinergic synapse?

A

A synapse where the neurotransmitter is acetylcholine

49
Q

Define cardiac muscle

A

Type of muscle found only in the heart. It has fewer striations than skeletal muscle and can contract continuously throughout life without stimulation by nerve impulses

50
Q

Define smooth muscle

A

Also known as involuntary or unstriated muscle, found in the alimentary canal and the walls of blood vessels. Its contraction is not under conscious control

51
Q

Define skeletal muscle

A

Muscle that makes up the bulk of the body and which works under conscious, voluntary control

52
Q

What are myofibrils?

A

Bundle of tiny muscle fibres called sarcomeres

53
Q

Define sarcomere

A

A section of myofibril between two Z-lines that forms the basic structural unit of skeletal muscle

54
Q

What is a muscle fibre?

A

A bundle of many myofibrils

55
Q

What is sarcoplasm?

A

Cytoplasm that surrounds muscle fibres

56
Q

What are the two protein filaments found in myofibrils and what is there structure?

A

Actin - Thin and consists of two strands twisted around one another
Myosin - Thick and consists of long rod shaped tails with bulbous projecting heads

57
Q

Summarise the locations in a sacromere

A

A Band - Location of myosin (no change in contraction)
I Band - Location between myosin (shortens in contraction)
H Zone - Location between actin (shortens in contraction)
Z line - End line of sarcomere (moves closer in contraction)

58
Q

What is tropomyosin?

A

A fibrous protein that surrounds the thin actin filament

59
Q

What are the two types of muscle fibres?

A

Slow twitch and fast twitch

60
Q

Summarise slow twitch fibres

A
  • Contract slower and less powerful but over longer period
  • Adapted for aerobic respiration to reduce lactic acid by having large store of myoglobin, rich supply of blood vessels and numerous mitochondria
61
Q

Summarise fast twitch fibres

A
  • Contract rapidly and produce powerful contractions for short periods of time
  • Adapted by having more myosin, higher concentration of glycogen, more enzymes involved in anaerobic respiration and store of phosphocreatine that generates ATP from ADP in aerobic conditions
62
Q

Define neuromuscular junction

A

A synapse that occurs between a neurone and a muscle/skeletal muscle fibre

63
Q

Why do muscles have multiple neuromuscular junctions?

A

To allow simultaneous contraction and hence rapid, powerful movement

64
Q

Why is acetylcholine broken down in muscle contraction?

A

To ensure the muscle is not over stimulated

65
Q

How do neuromuscular junctions differ from cholinergic synapses?

A
  • Only excitatory
  • Only linked neurones to muscles
  • Only motor neurones
  • End of action potential (end of neural pathway)
  • Acetylcholine binds to receptors on muscle fibre
66
Q

How are neuromuscular junctions and cholinergic synapses similar?

A
  • Both neurotransmitters transported by diffusion
  • Receptors causing influx of sodium ions
  • Sodium potassium pump for depolarisation
  • Enzymes break down neurotransmitter
67
Q

What are antagonistic pairs?

A

Muscles that pull in opposite directions. When one contracts the other relaxes

68
Q

What is the evidence for sliding filament mechanism?

A

When a muscle contracts, the following occurs to a sarcomere:

  • I band becomes narrower
  • Z lines move closer together
  • H zone becomes narrower
69
Q

How do we know contraction is not due to filaments shortening?

A

A band of myosin does not shorten in contraction

70
Q

What are the two types of protein that make myosin?

A
  • Fibrous making the tail

- Globular making bulbous heads

71
Q

Summarise how a muscle is stimulated

A
  • Action potential reaches neuromuscular junctions simultaneously
  • Calcium ion channels open and calcium ions diffuse into synaptic knob
  • Synaptic vesicles fuse with presynaptic membrane and release acetylcholine
  • Diffuses across cleft and binds with receptors causing depolarisation
72
Q

Summarise how a muscle contracts

A
  • Action potential travels in T tubules into sarcoplasm
  • Tubules in contact with sarcoplasmic recticulum which has actively transported calcium ions from sarcoplasm leading to low conc.
  • Opens calcium ion channels on sarcoplasmic recticulum and calcium ions diffuse down gradient into scarcoplasm
  • Ca2+ binds with troponin and causes tropomyosin molecules to move from blocking binding sites
  • ADP molecules attached to myosin heads bind to actin filament and form cross bridge
  • Myosin head changes angle and pulls actin filament whilst releasing ADP
  • ATP attaches to myosin head causing it to detach from actin
  • Calcium ions activate ATPase which hydrolyses ATP to ADP providing energy for myosin head to return original position
  • Myosin head attached with ADP molecule repeats as long as calcium ion conc remains high
73
Q

What occurs in muscle relaxation?

A
  • Calcium ions actively transported back into sarcoplasmic recticulum using energy from hydrolysis of ATP
  • Reabsorption of Ca2+ causes tropomyosin to block binding sites on actin
  • Myosin heads unable to bind and contraction stops
  • Anatagonistic muscles can now pull actin filaments out from between myosin
74
Q

What is the role of calcium in muscle contraction?

A

Moves tropomyosin to reveal binding sies and stimulates ATPase

75
Q

What is the role of ATP in muscle contraction?

A

Attachment of ATP causes myosin head to detach
Hydrolysis releases energy so myosin returns to original position
Actively transports Ca2+ back into sarcoplasmic recticulum

Biology - Unit 6 (6 decks)

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